


Trial and Error

by Smutmebby



Category: Undertale (Video Game)
Language: English
Status: In-Progress
Published: 2016-01-03
Updated: 2016-06-06
Packaged: 2018-05-11 11:55:57
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,336
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5625709
Author URL: https://archiveofourown.org/users/Smutmebby/pseuds/Smutmebby
Summary: <blockquote class="userstuff">
              <p>Sans discovers he may have sexual desires for the reader since they have come to stay with him, and tries to find a way that he could relieve those tensions.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> Fluff/ future NSFW smexiness; reader is unnamed but will be female in future smut.

Ever since they had decided to come live with him and Papyrus, life seemed to have been getting better. Sure it has taken Sans a few months to get over the anxiety over the thought of waking up to a reset, and he still occasionally woke up in the night sweating from the ghost of Papyrus from the last run - but those were few and far between and were solved by a quick dip into his brother’s room to make sure he was in fact still there.

The kid had been a great companion too, never complaining about his bad jokes and going along with him when he assured Pap that his cooking was in fact amazing, and yes of course they wanted spaghetti again! Hiding the fact that most nights Sans just ended up bringing them back some Grillby so they could eat once Papyrus had gone to sleep.

But lately, Sans had been feeling strange. Though the nightmares were dying down they were slowly being replaced with dreams of a different nature, one that he has never experienced before. They had been appearing to him, sometimes in innocent, gentle dreams that reminded him that this human was good. This human cared. But other times the dreams were rough, though he could never remember exactly what happened, he always woke up with a sense of longing that he couldn’t shake. He’d wake up and try and eat breakfast normally, but the second he locked eyes with them, he’d feel that redness rush up and he’d be forced to excuse himself for the rest of the day.

Alphys had called it “desire”; though of course Sans only explained it in an offhand way, opting to lie and say that the human was trying to explain it to him but didn’t know what it was called. Alphys had turned a darker shade and fidgeted for a few minutes for explaining:

“From what I’ve seen from human broadcasts, one human generally starts to feel like this when they’ve developed feelings for another human. G-generally this uh “redness” they spoke of would correspond with ..uh well desire.” Alphys coughed, waiting for Sans to speak. Of course Sans knew what it meant to want something - heck he always wanted Grillby’s - but this went far beyond a little hunger.

“Is it curable?” Sans asked in the end, not knowing how else to express his concern over having these feelings just stop. Alphys laughed, though she stopped when she saw Sans grimace.

“Oh well um… I wouldn’t be concerned if the human was feeling this. It would just mean that…” She hesitated, the confines of the office suddenly seemed to personal for this conversation. “Y-y’know, they…like someone. Romantically. Maybe even..s-s-sex -I mean you get it.” And with that Alphys had shooed Sans from her office saying she had plenty of important things to be doing and he should probably just mind his own business.

Sans spent most of that week away, he stayed at his sentry post well into the night and did his best to be out early before anyone was awake. He told his brother that he was just working overtime -that Undyne had asked him to work harder and he had finally taken it to heart. But he could tell the human didn’t buy it by the way they stared him down if he ever did come home. 

One day he came back well into the night, after everyone should have been in bed to find the human sitting on the couch watching T.V. He stood in the doorway shocked for a few moments- it had been a long day and he wasn’t sure how he would handle any form of confrontation at the moment.

“Hey kid, past your bed time ain’t it?” Sans shrugged off his coat, placing it on the table as he walked into the kitchen, avoiding the eyes he knew where watching him. “If you don’t sleep soon, you’ll be bone tired like me.” No response, not even a snort. He peeked over his shoulder to seen them standing in the doorway, watching him as he opened the fridge. He reached out for the ketchup bottle and noticed his arm was shaking a little.

“I know you’re worried about me, working hard and all” Sans stood up, carrying the ketchup bottle as he moved to walk past them; “I’ll take it easy, thanks for the concern pal -” His way was blocked by an arm, he looked into the living room, towards the door of his bedroom. If he could just lock himself up he would be safe.

They ask if they did something wrong, and Sans can tell tell they feel guilty about what’s been happening. He sighs and forces himself to turn toward them, leaning against the doorframe to put a nonchalant distance between the two of them.

“Listen, you didn’t do anything. Quit worrying or you’ll get wrinkles like me.” Sans points to his smooth skull and cracks a smile, relaxing a little when the human smiles at his joke. “There ya go.” He winks and ducks under the outstretched arm into the living room. “I’ll bring ya some burg tomorrow, we can watch some tv or something.” Sans ducked into his room as quickly as he could without seeming too eager, and behind the closed door he sighed a breath of relief.

The desire had flooded him, leaning up against the door frame, his figure gently touching their arm. 

He needed to do something about this fast. How did humans live with this?


	2. 10 Ways to Not Understand Humans

**Summary for the Chapter:**

> Sans finds trusted resources on human sexuality, and wonders how he ended up in this situation.

His dreams that night were warm, but not comfortable. Sans felt as if he was sitting on the edge of a very high place, that familiar feeling of wanting to jump - needing to fall off was coursing through him, but he didn’t know how high he was or what lay at the bottom. All he knew was that whatever was down there was hot, and he was already too warm where he was. Any closer and he feared he might melt away.

He didn’t join Papyrus or the human at the table that morning, opting to stay in his room, lying on the floor staring up at the ceiling in hope of forgetting the call to jump, the whirring of the treadmill drowning out the voices downstairs and the breeze from the garbage tornado cooling his bones. Only when he heard the knock on his door did he move, or rather teleport. At first he simply went to his post, but he had a feeling someone would be looking for him, so instead he took a walk back towards to ruins - to the door they had first come through.

For once he didn’t mind that they hadn’t left Snowdin yet, the constant snow was a welcome blurr to his already crammed thoughts. You didn’t have to think about snow - it was white, it was cold, and it fell no matter what. The surface was nice, and he loved the sun, but while they waited to find a suitable home up there, he was happy to be in a familiar space while he went through an unfamiliar problem.

Sans decided to try and map out the feelings he had: when had they started? He tried to remember back to the first wave of warmth he felt. One night he had had a particularly strong nightmare about the previous timeline, seeing his brother’s ashes, the anger as each one of his friends fell to the same blade. The endless battles, and then waking up to a reset. He had decided he wouldn’t sleep, had gotten it into his head that no sleep meant no reset. Out of determination to stay awake for the third night, he had wandered out the ruin again, promising only to take a small rest, but instead found himself asleep at the door within seconds of sitting against it. He woke up with a blanket wrapped around him, and the human keeping him company: he had worried them, they knew he hadn’t been sleeping well and had gone out looking for him when he failed to come home that night. There had been a warmth then, tickling the edge of his soul, but he had ignored it.

He recalled the warmth being pleasant though, not uncomfortable, but he couldn’t recall when it had become uncomfortable, only that every time it came back, it came back stronger and warmer.

Was it desire that he had? But what did he desire exactly? Sans could never recall truly desiring something more than sleep and food. Unless he had revenge on his mind, but he quickly discarded that thought - this human was good and he felt nothing like the sticky, black hole that anger filled him with. He was sure that if he could figure out what he wanted exactly, and find some way to fulfill that he would be fine to be around the human normally again, and maybe the feeling would even go away after a while. Though he would have to start with making an effort to act normal again, the longer Sans avoiding them the more they would go out of their way to figure out what was wrong, and eventually something awkward was going to be said or done.

He would start with movies tonight, just a good ol’ get together like they used to do on the harsher nights in Snowdin. Papyrus would be there, he would help offset the warmth. 

Sans stood up, wiping the snow of his shorts and smiling to the trees. It would be okay, if humans could live through this so called desire, he was sure Monsters with their magic and healing foods would be able to deal with it no problem. He would stop by Alphys’ and grab some human movies and see if he could get more information. So with a quick teleport he was standing outside of his friend’s laboratory, opting to knock instead of heading inside, Sans waiting until a voice called through the door.

“W-who is it?” Alphys as nervous as always called out.

“I think the line goes ‘who’s there?’” He called back, waiting as the door opened to reveal spectacled eyes peering from darkness. “Well I guess the joke is ruined now.” Sans tried to put on his most reassuring smile, he always forgot just how awkward Alphys was with guests.

“Sans, uh, d-did you come to ask about...um…” Alphys trailed off and Sans felt and bit of embarrassment rise in him.

“Movies that I could borrow?” He finished for her, moving his fingers inside his pocket in order to quell it. “How did you know, pal?” He waited for Alphys to say something, but she seemed to be preoccupied with staring at him, he glanced to the side and then back at her. “Is it cause I didn’t finish the knock knock joke?”

“O-oh! Uh, Movies! Y-yes, come in.” She disappeared from the crack, leaving it open for Sans to walk in.

The laboratory was even messier than usual, Sans has already lost track of where Alphys had gone when he closed the door behind him, carefully walking through the debris of a wall that had been broken but never repaired, stepping around what appeared to be trash but upon closer inspection...was still trash but from the surface.

“I have a lot of surface movies over here!” Alphys called from around a rather large pile of trash, “you can take any of them you like!” Sans casually walked around the pile and saw there was a smaller pile dedicated to the discarded DVDs that had probably been found in the dump over the years by Aphys in her pursuit of anime.

“Any recommendations?” Sans never really watched movies, anytime him, Papyrus and the kid sat down to watch them he would fall asleep quietly and wake up somewhere near the end. It was usually Papyrus that chose the movie anyway, and he wasn’t quite sure what the human liked to watch.

“There’s this really cool anime one that I have! Full of Magical Girls and sword fighting! It’s totally amazing!” Alphys gleamed at him, waiting in anticipation for Sans to agree enthusiastically, but all he could do was smile. “You’re right...Probably not your type.” She wandered away, seemingly put out and Sans turned his attention to the stack of movies.

He grabbed a few that looked interesting, some with explosions on the front, a couple that looked more colorful for Papyrus, he hoped that the human recognized at least one of them, maybe even liked one enough that they’d be excited to watch it instead of talking to him. Not that he didn’t want to talk...more that he didn’t know what he wanted. As he sorted through the pile almost mindlessly, he spotted one with a cover that stood out from the rest, mostly because it featured a male and female human. Naked. In the act of sexual reproduction.

Sans had seen it before of course, he was no stranger to human anatomy and the scientific way in which humans reproduced, but he wasn’t aware that they were documented in such a way. Perhaps it was a educational video? In the same way that the textbooks that fell down were? Although he knew that the act of sex was supposed to be a private thing, which made him start to put the video down, he wouldn’t want to see something that was so personal to the couple on the front.

What if it was educational though? He placed it down but kept his hand on it. Maybe he could learn about what he was feeling? Alphys had mentioned that desire could be sexual, so maybe this video mentioned desire? Perhaps he could watch it and learn how humans dealt with this feeling? He was torn between the obvious personal nature of the video and the possibility of answers when Alphys came back suddenly;

“I uh- also g-got this…” Sans swiftly hid the tape under the others he had chosen and turned to see Aplhys holding a thin magazine. “I-it might help..with uh well with your question…” She fiddled with the pages, not looking Sans in the eyes. “Y-yknow the uh d-desire that you m-mentioned.” Her cheeks had flushed a red color as she shoved the magazine in Sans’ direction.

Sans looked over the title, ‘Cosmopolitan’, it featured various titles of articles all over it, one of which was surrounded in hearts. “10 Ways to Tell If its More Than A Crush”.

“Humans use this magazine for advice on t-things like….d-desire..and stuff..” Alphys glanced down at the movies he had in his hand. “Good choice.” Flushing once more she turned and headed towards the elevator, leavings Sans alone with the magazine and his movies.

Sans placed the magazine at the bottom of the pile and rubbed the back of his skull. He supposed he would go home and read the magazine, maybe he wouldn’t need to watch the movie after all. He brought it just in case, and although he didn’t know exactly why, as soon as he was in his room he hid it under the bed. Not that anyone came in his room anyway, but he felt more secure knowing it was out of plain sight.

**Notes for the Chapter:**

> Second chapter! This should be more frequently updated now.


	3. Movies and touches

“1. You find yourself constantly making eye contact.”

Weren’t you supposed to make eye contact with humans? Sans didn’t think it was polite to stare anywhere else. You made eye contact when you talk to people, that’s how it was. He tried to think if perhaps he made less eye contact with Undyne, or Papyrus even, but he had never thought about it before.

“2. Your toes point towards them.”

Huh? What did that have to do with liking someone? Sans was sure there was no actually correlation between the way his toes pointed and how he was feeling, but he was only a skeleton - a human one mind you, but he was missing all the muscles and other things that made humans fleshy. It was possible one of his missing components would have been responsible for that function.

“3. You have trouble sleeping when they’re close.”

Okay, he was having trouble sleeping. But that was mostly due to the weird dreams he was having. Maybe the magazine meant the weird dreams, everybody dreamed as far as Sans knew, so it would make sense that it could be a common thing across species, to experience lack of sleep due to strange dreams when you felt desire.

“4. You find yourself touching them more often.”

Sans could safely say he didn’t line up with that criteria, not that he touched anyone to begin with but he was particularly careful about not touching them. Somehow the thought didn’t comfort him, but rather he felt a little warmer thinking about it.

He closed the magazine and tilted his skull against the wall. He was overthinking things, if a ‘crush’ was what these things led up to, he was sure he didn’t have that. It was a human thing, monsters didn’t get ‘crushes’. Sure they bonded, but nobody had ever talked about desire, and he was sure he would have learned about it somewhere down the line if monsters felt that. The magazine said crushes were normal, something that happened when you found someone attractive and wanted to be near them. Sans guessed that would be the same things as monsters when they matched with another’s soul and felt the need to be together with the other, but none of this other stuff made sense to him. Why did humans go through so many levels of attraction? Didn’t they know when they were bonding with someone? It seemed pointless to have a magazine help you distinguish from whether you actually liked someone or not.

Then again, he was doing just that.

Frustrated with himself he tossed the magazine into the garbage tornado, if it was a human thing he was feeling then he was going to have to try and understand it - and to do that he would have to try and observe the symptoms and figure out what was causing them. Treat it like a science experiment, that was something he was more familiar with. Document, theorize, and test.

With that in mind he left his room, he had after all promised to host a movie night, and he did feel bad about avoiding the kid so much - they hadn’t done anything to him directly after all. He found the human sitting on the couch, surfing through some of the stations they got in the undergound, but they hadn’t heard anything from Papyrus.

“Hold on, I’ll ring him.” Sans took a seat next to them, pulling out his phone and using his speed dial to call his brother. It only took half a ring before he answered.

“SANS! DO YOU REQUIRE AID OF SOME KIND?” Sans smiled and lifted his feet to rest on the side table.

“Yeah, I can’t find my phone.”Sans closed his eyes, trying to act more like his normal self.

“SANS! YOU’RE ALWAYS LOSING THINGS! WHO DID YOU CALL LAST??” Sans opened his eyes to watch his friend as they looked through the selection of movies he had brought down, they carefully read the back of each DVD so Sans could tell they hadn’t seen any of them.

“I think I called you last bro.” Sans watched as their eyes squinted, their tongue poking out from the edge of their lips as they concentrated on the small print. He felt the tingle on the edge of his soul again.

“OF COURSE YOU DID, WHO ELSE WOULD YOU CALL OTHER THAN THE GREAT PAPYRUS!” Sans tried to smile but it was caught in the warmth rising in his chest.

“Heh, yeah. Can you come home and help me look for it? Me and the kid were gonna watch a movie after.” Sans closed his eyes, plastering his trademarked smile to his face as he waited for the enthusiastic response.

“THE GREAT PAPYRUS HAS A BETTER IDEA! I WILL CALL YOUR PHONE SO YOU MAY FIND IT!” Before he could protest Sans’ phone had already disconnected, and before he could even pull it from his head is rung again with Papyrus’ signature ring tone. He contemplated not answering it, but decided that his brother would understand the joke eventually and would be rather upset with him if Sans decided to ignore him on purpose.

“Yo.”

“AHA! YOU HAVE LOCATED YOUR PHONE! MY JOB HERE IS DONE!” The click of the phone was almost deafening as Sans was hung up on. Silence hung in the air as they looked at him expectantly, waiting for Sans to decide what to do. Not that he had many options.

With a strange pounding in his chest, he reached over and carefully took the movie from between their finger and read the back of it.

“Are you sure you wanna watch this one? Seems a bit boring.” Sans eyed the pictures depicted on the case, he wasn’t sure there was a single calm scene shown. All of them were full of explosions and fighting. They rolled their eyes and took the case from him, getting up to place it in the DVD player. While trying not to stare at them Sans formulated his plan: Just watch the movie, make a few jokes here and there to make it seem normal, then call it a night. If he started to feel weird he would note why and remember to write it down later to keep track of it.

They grabbed some chips from the kitchen and Sans settled in the couch, placing his arms on the back ledge and sinking into his hoodie. He had done this plenty of times before, he knew it didn’t have to be awkward. He definitely did not have to act the way he had been, the poor kid already felt guilty, he could tell by the way they kept peeking at him from the corner of their eye. Was he making too much eye contact? He should stop looking at them. Sans focused his attention mercilessly on the television.

What were the other notes? Pointed toes. He stared at his feet, but they were up on the table. What counted as pointing towards them? They really could only point in one direction. He was being ridiculous he decided, they were just enjoying a movie with a friend and that’s what he needed to do too.

Half of the movie had gone by without incident, Sans found he could focus on what was happening on the screen and still make a few comments that earned him relaxed smiles from his friend. He was doing well to restore faith that everything was as it was: until they leaned back a little and Sans found his hand on the back of their head. He had touched their head before of course, but this seemed so much more intimate than the pat on the head he was used to doing. He expected them to move away when they noticed his hand, but they didn’t. Perhaps they hadn’t noticed? They did seem really into the movie. Sans gave a small scratch with his hand, hoping they would notice and move away from him, but instead, as their hair wrapped around his bones, they gave a sigh and leaned into it more.

Now he was in trouble, the heat had started to rise with the little sigh and Sans wasn’t sure he wanted to pull his hand back. Their hair was so soft, and as it wove in and out of his knuckles he felt the warmth spreading through him entirely. As if they were drawn to it, they leaned into him, resting their head on his rib cage and suddenly Sans was very thankful that he did not have a heart or skin to betray how he felt.

He dropped his hand to their shoulder, feeling a strangled tension where his heart would be. He gave them a tentative side hug and their inquisitive look make his soul stop for a moment. He noticed that the movie had ended and wondered how long they had been like this in silence.

“Good choice, my favorite part was the explosion.” He chuckled slightly, as they pointed out there has been at least 4. Neither of them made an effort to move and Sans could feel the warmth being replaced by a familiar hum, one that came with his magic. Slightly panicked by the change Sans slid his arm back and made a show of stretching. “Welp, it's been real kid, but I’m bone tired, think I should hit the sack.” 

As he stood up he felt a soft hand slide around his wrist, glancing down he saw them looking up at him worriedly. They were concerned, was he sick? Was he not sleeping well? They heard him having nightmares last night and were concerned when he didn’t show up to breakfast. Sans sighed and placed his other hand on their head.

“I’m not sick…” He debating asking them, but he wasn’t sure if he could describe it. If Alphys’ reaction was any indication, he was also sure this was something he shouldn’t share. “A little tired is all, I’ll make sure to get more sleep.” He gave them one more scratch on the head and quickly excused himself to his room, feeling the hum of magic in his bones that he hoped they couldn’t detect.

Now he was confused, if his desire was a human thing, why was it sparking his magic? Why would his magic automatically respond, when normally he had to concentrate to call on it? As he stood in his empty room he felt the humming slow and eventually stop, for the rest of the night he waited to see if it would come back, but it never did.

**Notes for the Chapter:**

> Please excuse the perspective, I find that I'm terrible at writing Sans as he is generally supposed to be, and my pun game is weak. However, I hope you are enjoying the concept of a sexually unaware Sans!

**Author's Note:**

> This first chapter was kinda short, but I'll be sure to write longer ones in the future! Was just getting into the feel of this fic.


End file.
